1. Department of Preventive Medicine, Armed Forces Medical Command, Seongnam, South Korea.
2. Occupational Safety and Health Research Institute, Ulsan, South Korea.
3. Department of Preventive Medicine, Seoul National University College of Medicine, Seoul, South Korea.
4. The Institute for Occupational Health, Yonsei University College of Medicine, Seoul, Korea.
5. Department of Preventive Medicine, Yonsei University College of Medicine, Seoul, Korea.